A. Field of the Invention
This invention relates to valves, and more particularly to shuttle valves. The invention is an improvement upon shuttle valves of the type made and sold by applicant's assignee, Gilmore Valve Company, which is the owner of the other U.S. patents for improved shuttle valves including U.S. Pat. Nos. 3,533,431 and 4,253,481.
B. Description of the Prior Art
Shuttle valves have been used for many years to control the flow of gases as in U.S. Pat. Nos. 1,529,384 and 2,408,799. Other shuttle valves have been used to control the flow of liquids as in U.S. Pat. Nos. 1,686,310 and 1,795,386.
Shuttle valves used to control hydraulic fluid, particularly those used in underwater oil field equipment, must be designed taking into consideration working pressures, up to several thousand psi and flow rates of up to several hundred gpm. It is especially important that underwater shuttle valves used in connection with operation of subsea blowout preventers (BOPs) have a long trouble-free life because of their inaccessibility. The differential pressure on the shuttle often results in high momentum as it moves from one valve seat to another. When a shuttle contacts a valve seat, the repeated impact can break or crack the cage or cause it to be warped, and can otherwise disrupt proper valve operation.
One way to address the problem of shuttle impact is to lighten the shuttle and provide rubber cushions in the form of thick sealing elements as shown in U.S. Pat. No. 3,038,487. Yet another way of addressing shuttle impact is a hydraulic cushion as shown in U.S. Pat. No. 4,253,481 owned by applicant's assignee. The hydraulic cushion discussed above is similar to the action of a hydraulic cushioned slush pump valve as shown in U.S. Pat. Nos. 2,197,455 and 2,605,080. U.S. Pat. No. 2,654,564 discloses a metal to metal seat to take the axial load imposed on the shuttle and thereby to limit the pressure on the rubber seal ring so that the rubber is prevented from being overloaded, cut or extruded by the action of high pressure fluid.
The shuttle valve disclosed in U.S. Pat. No. 4,253,481 was sold for many years by Gilmore Valve Company for use with underwater oil field equipment. This prior art valve shuttle valve was limited to two inputs and was relatively expensive to manufacture. To overcome some of these limitations, Gilmore introduced the Mark I shuttle valve in 1997 as shown in FIG. 1 of the drawings. The Mark I relied upon two elastomeric o-rings mounted around the central flange of the shuttle to achieve a seal. The end portions of the shuttle were relatively thin and were prone to cracking because of shuttle impact. In addition, the o-rings were sometimes cut or blown off due to operational pressures and flow rates.
In order to overcome some of the limitations of the Mark I, Gilmore developed a retrofit design known as the Mark II which was introduced in 1998 as shown in FIG. 2 of the drawings. The Mark II design included an increased thickness of the end portions or cage, a decrease in hole size, larger o-rings which were stretched around the shuttle and a pair of plastic teflon bearings to center the shuttle and reduce vibration as it traveled back and forth. The Mark II eliminated many of the problems of the Mark I; however, at the highest operational flow rates, o-rings were still lost. The present invention is designed for operation at 5,000 psi; the 1/2 inch model is designed for an 80 gpm flow rate, the 1 inch model is designed for a 250 gpm flow rate and the 11/2 inch model, is designed for a 350 gpm flow rate.
In an effort to overcome the limitations of the Mark I and Mark II, applicant has developed an improved design which is the subject of the present invention. In order to overcome some of the problems associated with elastomeric seals, the present invention has eliminated such seals and now relies upon a metal to metal seal. The metal to metal seal of the present invention is progressively coined because of repeated contact between opposing tapered sealing surfaces surrounding a central flange on the shuttle and opposing metal valve seats.
The present invention includes alternative embodiments having a modular design that allows the components to be stacked one upon the other to receive more than two inputs. Another stackable, multi-input valve is disclosed in U.S. Pat. No. 4,467,825. This design uses a plurality of spool valve members to direct a superior fluid input signal to the outlet.
The present invention is less expensive to manufacture than prior shuttle valves sold by Gilmore Valve Company as disclosed in U.S. Pat. No. 4,253,481. Alternative embodiments of the present invention allow the shuttle valve to receive 3 or more inputs which was not possible with the shuttle valve disclosed in U.S. Pat. No. 4,253,481. In addition, the present invention overcomes the limitations of the Mark I and Mark II discussed above.
In emergency situations or during testing, it may be necessary to close the subsea BOPs using a remote operated vehicle (ROV). The ROV is an unmanned submarine with an on-board television camera so the ROV can be maneuvered by topside personnel on board a ship. The ROV is equipped with a plug that stabs into a receptacle on the ROV docking station on the lower marine riser platform (LMRP). The LMRP sets on top of the BOPs. A hose runs from the receptacle on the ROV docketing station to a biased shuttle valve.
In an emergency or during testing, the ROV is maneuvered to stab into the receptacle on the ROV docking station. The ROV injects hydraulic fluid at relatively high pressures (greater than 1,000 psi) and relatively low flow rates into the hose to the biased shuttle valve to close the BOPs. Gilmore Valve Company has sold a flow biased shuttle valve to work with the ROV, but it has operational limitations. This prior art flow biased shuttle valve was flow activated and it needed the following minimum flow rates to activate: one-half inch model, 5 GPM; 1-inch model 20 GPM and one and one-half inch model 50 GPM. Some ROVs on the market may not be able to produce sufficient flow rates in the larger sizes to activate the prior art Gilmore flow biased shuttle valve.
In order to address this need, a pressure biased shuttle valve was developed that operates on pressure, not flow. The pressure biased shuttle valve of the present invention needs a minimum operating pressure of 1000 psi and little or no flow. Most, if not all ROVs currently on the market, can produce operational pressures well in excess of 1,000 psi, and thus can operate the pressure biased shuttle valve of the present invention. The pressure biased shuttle valve uses the coining technique to achieve a metal to metal seal.
Some prior art shuttle valves had problems with switchback. This phenomena occurs only on return flow and is the result of fluid momentum shifting the shuttle after closing pressure is relieved and prior to opening pressure being applied. This results in an indefinite flow path for return flow. Most return flow paths in the closing circuit exhaust to the ocean, so usually this does not create an operating problem. The exception to this is when one of the possible return paths is an ROV port. Such ports are commonly plugged to prevent saltwater ingress into the system. If the return flow becomes inadvertently switched to a plugged ROV port, it will substantially increase the opening time of the BOP. The present invention was developed to reduce switchback. The present invention employs a spring which biases the return flow to the non-biased port. The biased port is energized by pressure, permitting operation with low volume pumps employed on ROV's. In addition, the spring is preloaded so that saltwater may exceed the ambient hydraulic system pressure by up to 100 psi without leakage of salt water into the hydraulic system.